Obstacles to a comprehensive definition

Diaz-Paniagua has noted that, in order to "create an effective legal regime against terrorism, it would be necessary to formulate a comprehensive definition of that crime that, on the one hand, provides the strongest moral condemnation to terrorist activities while, on the other hand, has enough precision to permit the prosecution of criminal activities without condemning acts that should be deemed to be legitimate. Nonetheless, due to major divergences at the international level on the question of the legitimacy of the use of violence for political purposes, either by states or by self-determination and revolutionary groups, this has not yet been possible."[21] In this sense, Bassiouni notes:

"to define "terrorism" in a way that is both all-inclusive and unambiguous is very difficult, if not impossible. One of the principal difficulties lies in the fundamental values at stake in the acceptance or rejection of terror-inspiring violence as means of accomplishing a given goal. The obvious and well known range of views on these issues are what makes an internationally accepted specific definition of what is loosely called "terrorism," a largely impossible undertaking. That is why the search for and internationally agreed upon definition may well be a futile and unnecessary effort."

The political and emotional connotation of the term "terrorism" make difficult its use in legal discourse. In this sense, Saul notes that:

"Despite the shifting and contested meaning of "terrorism" over time, the peculiar semantic power of the term, beyond its literal signification, is its capacity to stigmatize, delegitimize, denigrate, and dehumanize those at whom it is directed, including political opponents. The term is ideologically and politically loaded; pejorative; implies moral, social, and value judgment; and is "slippery and much-abused." In the absence of a definition of terrorism, the struggle over the representation of a violent act is a struggle over its legitimacy. The more confused a concept, the more it lends itself to opportunistic appropriation."

The sectoral approach

In order to elaborate an effective legal regime to prevent and punish international terrorism, rather than only working on a single, all-encompassing, comprehensive definition of terrorism, the international community has also adopted a "'sectoral' approach aimed at identifying offences seen as belonging to the activities of terrorists and working out treaties in order to deal with specific categories thereof". The treaties that follow this approach focus on the wrongful nature of terrorist activities rather than on their intent:

On the whole, therefore, the 'sectoral' conventions confirm the assumption that some offences can be considered in themselves as offences of international concern, irrespective of any 'terrorist' intent or purpose. Indeed, the principal merit of the 'sectoral approach' is that it avoids the need to define 'terrorism' of 'terrorist acts' (...) So long as the 'sectoral' approach is followed, there is no need to define terrorism; a definition would only be necessary if the punishment of the relevant offences were made conditional on the existence of a specific 'terrorist' intent; but this would be counter-productive, inasmuch as it would result in unduly restricting their suppression.